Vehicle brake lathe with variable speed motor

ABSTRACT

The present invention relates to on-car brake lathes configured for resurfacing brake rotor components, and in particular, to improved on-car brake lathes configured with a controlled variable speed drive system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to, and claims priority from, U.S.Provisional Patent Application Ser. No. 60/489,639 filed on Jul. 24,2003, and herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates to automotive vehicle brake lathesconfigured for resurfacing brake rotor components, and in particular tovehicle brake lathes utilizing variable speed drive motors.

One of the main components of a vehicle wheel braking system employingdisk brakes are the brake disks, or brake rotors, which provide a solidrotating surface against which the stationary brake friction pads areclamped or compressed to generate a frictional force, slowing therotational movement of the brake disks or brake rotors and theassociated vehicle wheels. The brake disks or brake rotors are subjectedto repeated and substantial frictional forces by the brake frictionpads, and over time, become worn. Uneven application of braking force,debris, or uneven frictional surfaces on the brake friction pads canresult in the formation of grooves, channels, or scratches in thesurfaces of the brake disks or brake rotors. Repeated heating andcooling of the brake disk or brake rotor resulting in extremetemperature variations can additionally result in the lateral warping ofthe brake disk or brake rotor.

A worn or warped brake disk or brake rotor may be resurfaced by cuttingor grinding to provide a uniform smooth brake friction pad contactsurface if sufficient brake disk or brake rotor material remains toprovide an adequate braking surface without compromising the structuralintegrity of the vehicle braking system. However, once a brake disk orbrake rotor has been worn below a minimum safe thickness, it is unableto safely dissipate the heat generated by a brake application, and mustbe replaced.

To provide for a uniform surface, any abnormalities in the brake disk orbrake rotor, such as a lateral warping must be detected and removedduring the resurfacing procedures. An additional source of lateralwarping defects in a brake rotor or brake disk is often over tightenedattachment bolts or an uneven mounting surface onto which the brake diskor brake rotor is secured in the vehicle wheel assembly. If the brakedisk or brake rotor is removed from the vehicle wheel assembly for aresurfacing operation on a fixed or “bench” brake lathe anyabnormalities or defects resulting from the mounting of the brake diskor brake rotor to the vehicle wheel assembly may not be accuratelyidentified or corrected during the resurfacing procedure. Accordingly, avariety of brake resurfacing machines or brake lathes have beendeveloped to resurface brake disks and brake rotors while they remainmounted to the vehicle wheel assembly.

Brake resurfacing machines or brake lathes configured to resurface brakedisks and brake rotors mounted to a vehicle wheel assembly are commonlyreferred to as on-car brake lathes. One example of an on-car brake latheis the OCL-360 brake lathe sold by Hunter Engineering Co. of Bridgeton,Mo. By eliminating the need to remove the brake disk or brake rotor fromthe vehicle wheel assembly, the overall efficiency of the resurfacingprocedure is improved, and the chances for operator induced error arereduced.

Traditionally, on-car and bench brake lathes, such as the BL501/BL505off-car brake lathe sold by Hunter Engineering Co. of Bridgeton, Mo.,utilize motors or drive systems configured for operation at a fixedspindle RPM and feed rate. During rotor cutting or resurfacing, aresonance or vibration, commonly referred to as “chatter”, can developbetween the rotor cutting tools and the rotor surface, resulting at bestin an uneven resurfacing of the brake rotor, or at worst, in severedamage to the rotor surface or rotor cutting tools themselves.Accordingly, the fixed spindle RPM and feed rates in traditional on-carand bench brake lathes are selected to be below the rates at which theresonance or vibration is likely to occur. However, since the rates atwhich the resonance or vibration are likely to occur vary for differenttypes of brake rotors, there is a need for on-car and bench brake latheshaving improved drive motor systems, which are capable of varying thespindle RPM during the resurfacing of a rotor and, optionally, the feedrate, up to a maximum rate at which a desired brake rotor resurfacingquality can be achieved, thereby reducing operator time require toresurface a brake rotor and providing enhanced safety features, such asautomatic motor speed reduction or shutoff during abnormal operatingconditions.

Some vehicles are equipped with locking differentials in the vehicledrive train that engage when a difference in wheel rotational speed fromone side of the vehicle to the other reaches approximately 100 RPM. Whenthe locking mechanism engages, as may occur during rotation of a brakerotor by an on-car brake lathe, the resulting change in rotationalresistance can violently rotate the entire on-car lathe body. It isdesirable to provide an on-car brake lathe with safety featuresconfigured to automatically stop the lathe rotation if a suddenresistance is encountered in the cut.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, the present invention is an improved brake lathe systemfor the resurfacing of vehicle brake rotors. The improved brake lathesystem is configured with a variable speed drive system and controllerfor regulating the rotor cutting rate.

In an alternate embodiment, a brake lathe of the present inventionincorporates a variable speed spindle motor as a drive system. Thevariable speed spindle motor may be a direct current motor with a pulsewidth modulation controller or an SCR controller, or an AC motor with avector drive, inverter drive, or a Volts/Hertz drive. The variable speedspindle motor is configured to drive the output spindle at a variableRPM and may optionally provide a variable linear feed rates for thecutting head when resurfacing a brake rotor.

The foregoing and other objects, features, and advantages of theinvention as well as presently preferred embodiments thereof will becomemore apparent from the reading of the following description inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 is a perspective view of an on-car vehicle brake lathe secured toa transport trolley;

FIG. 2 is a perspective view of the on-car vehicle brake lathe of FIG.1, without the transport trolley;

FIG. 3 is a view of the operator interface;

FIG. 4 is an exploded view of the electrical component enclosure;

FIG. 5 is a side-sectional view of the electrical component enclosure ofFIG. 3;

FIG. 6 is a block diagram of the components of the processor board ofthe on-car brake lathe; and

FIG. 7 is a block diagram of motor control circuitry of the on-car brakelathe.

Corresponding reference numerals indicate corresponding parts throughoutthe several figures of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description illustrates the invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the invention, describes severalembodiments, adaptations, variations, alternatives, and uses of theinvention, including what is presently believed to be the best mode ofcarrying out the invention.

Referring to FIGS. 1 and 2, an on-car brake lathe 10 of the presentinvention is shown mounted to a transport trolley 12 for positioningadjacent a vehicle to be worked on (not shown). The on-car brake lathe10 includes a support structure 14, onto which is mounted a variablespeed drive system. The variable speed drive system preferably includesa variable speed spindle motor 16, an adjustable cutting head 18, and anoutput spindle 20. The variable speed spindle motor 16 is coupled to theoutput spindle 20 through a conventional drive mechanism (not shown)contained within the support structure 14, to rotate the output spindle20 about a drive axis DA, and to linearly feed the cutting head 18 andcutting tool holders 19 carrying cutting tips 21 through a predeterminedcutting range CR. An aligning joint 22 is secured to the output spindle20, concentric with the drive axis DA, adapted to couple the outputspindle 20 to a vehicle wheel hub or brake assembly.

Additionally included on the support structure 14 is an electricalenclosure 24. An operator interface 26 is mounted to the electricalenclosure 24. The operator interface 26, shown in FIG. 3, preferablyincludes at least a bar graph LED display 28 and a numerical LED display30, and may optionally include one or more additional visual displayelements 32 configured to provide the operator with informationassociated with the operation of the on-car brake lathe 10. For example,multiple visual display elements 32 in the form of single LED lights maybe disposed on the operator interface 26 to assist an operator inperforming a runout compensation procedure when coupling the on-carbrake lathe 10 with a vehicle brake assembly, or to indicate thepresence of a chatter condition during a resurfacing procedure.

Operator input controls 34 are additionally included on the operatorinterface 26.

The operator input controls 34 preferably include at least a startbutton 34A, a stop button 34B, a spindle speed control knob 34C, acompensation button 34D, and a runout test button 34E.

Included within the electrical enclosure 24, as shown in FIG. 4 and FIG.5 is a processor board 36 and motor controller 38. The processor board36 incorporates a microprocessor 40. The microprocessor 40 may be amicro-controller, digital signal processor, or other logic circuithaving sufficient capacity to control the functions of the on-car brakelathe 10, and is configured to access and execute instruction setsstored in a suitable electronic memory 40A, such as a RAM, ROM, EPROM,or EEPROM. The electrical enclosure 24 preferably further includes aheat sink 38A associated with the motor controller 38, a mounting shaft39 for connecting to the on-car brake lathe 10, and an adjustment knob41.

As shown in FIG. 6, the microprocessor 40 is operatively coupled to themotor controller 38 and to an LED drive circuit 42 for controlling theoperation of the LED bar graph display 28, LED numeric display 30, andany additional visual display elements 32. The microprocessor 40 isadditionally operatively coupled to receive signals from the operatorinput controls 34. One or more data lines 44 operatively couple themicroprocessor 40 to the motor controller 38. The data lines 44 mayoptionally include a digital to analog converter circuit 46, and/or ananalog optical isolator circuit 48, depending upon the particular inputrequirements of the motor controller 38. The motor controller 38 is inturn, coupled to the variable speed spindle motor 16 to provideelectrical power to the motor windings (not shown), thereby controllingthe motor output.

As is further seen in FIG. 6, the microprocessor 40 may be operativelycoupled to receive input from, or exchange data with, one or moreadditional components of the on-car brake lathe 10 during operation ofthe on-car brake lathe 10. These components may include, but are notlimited to, a motor shaft rotational position encoder 50, a lathe tiltangle sensor 52, an accelerometer 54, a communications circuit 56 suchas an RS422 port, or other optional encoder circuits 58. Preferably, asuitable power supply 60 for the microprocessor 40 and associatedcircuits, such as a transformer or AC/DC converter, is provided on theprocessor board 36.

Preferably the microprocessor 40 is configured to monitor the rotationalspeed of the variable speed spindle motor 16 using the motor shaftrotational position encoder 50, which is operatively coupled to theshaft of the motor engaged with the output spindle 20. A representationof the rotational speed of the motor 16 may be displayed to an operatorby the microprocessor 40 using either the LED bar graph display 28 orthe LED numeric display 30. The microprocessor 40 regulates the inputsignal representative of a desired rotational speed to the motorcontroller 38, and adjusts the input signal in order to reach ormaintain a desired rotational speed or torque of the output spindle 20.The output signal of the motor shaft rotational position encoder 50 isfurther utilized by the microprocessor 40 to monitor and control therotational position of the output spindle 20 about an arc of less than360 degrees, such as for use during runout compensation procedures.

In addition to providing control signals to the motor controller 38 inresponse to signals from the motor shaft rotational position encoder 50,the microprocessor is preferably configured to provide motor speedcontrols signals in response to signals received from a potentiometer 42coupled to the spindle speed control knob 34C, permitting an operator tomanually indicate or select a desired rotational speed for the motor 16and/or output spindle 20. A representation of either the actualrotational speed of the motor 16, or the desired rotational speed asindicated by an operator using the spindle speed control knob 34C, maybe displayed on either the LED bar graph display 28 or the LED numericdisplay 30 by the microprocessor 40.

During operation, the on-car brake lathe 10 is detachably secured to avehicle wheel brake rotor on a vehicle axle in a conventional manner. Anadapter (not shown) is initially secured to the vehicle wheel brakerotor using the vehicle wheel lug nuts or retaining bolts (not shown).Next, the on-car brake lathe 10 is moved into position such that thealigning joint 22 and drive axis DA are substantially co-linear with acentral axis of the rotor-mounted adapter, corresponding to a rotationalaxis of the vehicle wheel brake rotor. A threaded retaining shaft (notshown) is passed axially through the support structure 14 and outputspindle 20, and engaged with an axial threaded receiving bore (notshown) in the rotor-mounted adapter. Tightening of the threadedretaining shaft seats the rotor-mounted adapter against the aligningjoint 26, and secures the on-car brake lathe 10 to the vehicle wheelbrake rotor to be resurfaced, enabling the vehicle wheel brake rotor tobe rotated by the variable speed spindle motor 16 of the on-car brakelathe 10.

Control of the variable speed spindle motor 16 of the on-car brake lathe10 to drive the output spindle 20 and the linear movement of theadjustable cutting head 18 is enabled by the microprocessor 40,responsive either to preset instructions or to operator commandsreceived from the operator interface 26, and the motor controller 38.The variable speed spindle motor 16 may be any of a variety ofcontrollable variable speed motors, such as an alternating current (AC)motor with a vector drive or a Volts/Hertz drive control or a directcurrent motor with a pulse width modulation drive controller or an SCRdrive controller. In the preferred embodiment, the variable speedspindle motor 16 is a 3-phase alternating current, 60 Hz, 2 poleinduction motor, such as the Franklin Electric Model No. 1313007434,rated at 1.5 horsepower, and the motor controller 38 is a MinarikVFD05-D230-PCM AC Volts/Hz drive controller. In alternate embodiments,the variable speed spindle motor 16 may be a single-phase permanentssplit capacitor motor, a shaded pole motor, or a synchronous motor.

In the preferred embodiment, the variable speed spindle motor 16 iscontrolled by the Volts/HZ drive motor controller 38 in response to a1-10 Volt reference signal conveyed to the motor controller 38 by themicroprocessor 40 on the control line 44 coupled between themicroprocessor 40 and the motor controller 38. The motor controller 38varies the output speed of the variable speed spindle motor 16 byaltering the frequency of alternating current supplied to the variablespeed spindle motor 16 from an external power source. Preferably, thefrequency is varied between 40 Hz-80 Hz to achieve a correspondingoutput speed of the motor 16 between 60-120 RPM. The microprocessor 40preferably can direct the motor controller 38 to regulate the outputspeed of the motor 16 to less than 60 RPM, as well as to control therotation of the motor 16 through less than one complete revolution, asmay be required for special operations or runout compensation prior tostarting a rotor resurfacing operation.

To maintain a constant flux in the variable speed spindle motor 16, thevoltage supplied to the variable speed motor 16 is additionallyregulated by the motor controller 38, incrementally increasing at aconstant rate from 0 Volts at 0 Hz, to a maximum constant voltage at 60Hz and above.

In the preferred embodiment, alteration of the frequency of thealternating current supplied to the variable speed spindle motor 16 bythe motor controller 38 in response to the reference signal from themicroprocessor 40 occurs in three phases. Initially, incoming voltagesupplied to motor controller 38 from the external power source isdoubled, and supplied alternating current power is converted to directcurrent power utilizing a bridge rectifier circuit included on the motorcontroller 38 board. Next, a capacitor circuit also included on themotor controller 38 board is utilized to smooth remaining ripples in thedirect current power left over from the alternating current sine wavepatterns. Finally, the motor controller 38 utilizes an inverter circuitto provide pulse width modulation to recreate an alternating currentsine wave at the desired frequency and voltage from the direct powerwaveform. Those of ordinary skill in the art will recognize that thebridge rectifier circuit, capacitor circuit, and inverter circuit are ofconventional design, and hence are not specifically illustrated in theFigures.

The frequency of the pulse width modulations is varied in response tothe reference voltage from the microprocessor 40, utilizing a pluralityof transistor circuits, thereby supplying a variable voltage to thevariable speed spindle motor 16. Thus, alternating current having avoltage and frequency regulated by the motor controller 40 is suppliedto the variable speed spindle motor 16. The rotational speed and torqueof the variable speed spindle motor 16 is correspondingly proportionalto the supplied alternating current voltage and frequency.

In an alternate embodiment, the variable speed spindle motor 16 of theon-car brake lathe 10 is a pulse-width-modulation (PWM) controlleddirect current motor. A 30 Hz watchdog pulse is supplied to the motorcontroller 38 from the microprocessor 40, together with a signalrepresentative of a settable duty cycle, which is interpreted by themotor controller 38 as a linear function of the desired “torque”, suchas shown in U.S. Pat. No. 6,324,908 to Colarelli, III et al. and in U.S.Pat. No. 6,386,031 to Colarelli, et. al. for vehicle wheel balancerapplications. The motor controller 38 is configured to regulate theoutput speed and torque of the variable speed spindle motor 16 bycontrolling the flow of direct current to the motor windings from anexternal power source.

For example, as shown in FIG. 7, the motor controller 38 may include aset of four drive transistors Q1, Q2, Q3, and Q4 connected to providedirect current to the windings of the variable speed spindle motor 16selectively with each polarity. Specifically, a first transistor Q1 isconnected to supply direct current from a bridge rectifier circuitreceiving alternating current from an external power source to one sideof the windings of the variable speed spindle motor 16. When a flow ofdirect current is supplied through the first transistor Q1 to thewindings, the circuit is completed through the windings and a secondtransistor Q4 to an electrical ground. This causes the windings of thevariable speed spindle motor 16 to be energized so as to cause rotationof the drive shaft in a first rotational direction. Similarly, when thefirst two transistors Q1 and Q4 are rendered non-conductive, and thesecond two transistors Q2 and Q3 are conducting direct current, thewindings of the variable speed spindle motor 16 are energized with theopposite polarity, resulting in rotation in a second direction. It ispreferred that the direction of rotation of the variable speed spindlemotor 16 be controlled by the pulse width modulation of the directcurrent to the transistors. A duty cycle of 50% causes the directcurrent to flow through the motor windings in both directions in equalamounts. By providing a suitably high pulse rate, the motor 16 hasinsufficient time to respond to the rapidly reversing currents,resulting in zero motor rotational velocity. Under these conditions, themotor 16 actively holds the output shaft in a current rotationalposition, providing, in effect, a “detent” function for the outputspindle 20.

A duty cycle of less than 50% causes rotation of the motor 16 and outputspindle 20 in a first direction. As the duty cycle decreases from 50% ,the torque in the direction of rotation increases. Similarly, a dutycycle of more than 50% causes rotation of the motor 16 and outputspindle 20 in the second direction. As the duty cycle increases from 50%, the torque in the direction of rotation increases. A 0% duty cycleachieves maximum torque in a first rotational direction, while a 100%duty cycle achieves maximum torque in the second rotational direction.

Whatever variable speed drive system is used with a variable speed drivemotor 16, it preferably has interface circuits 39A, 39B, and 39C for thedrive enable, “torque” input, and watchdog inputs respectively from themicroprocessor 40. These signals are supplied to a control logic circuit41 which performs necessary logic functions, as well as conventionaldeadband, and current limit functions. Circuits to perform the functionsof logic circuit 41 are well known. The current limit function of logiccircuit 41 depends upon the current measured by the current senseresistor RS, the voltage across which is detected by a current limitdetection and reference circuit 43.

Logic circuit 41 has three outputs. The first, a drive fault line DF, isused to signals the microprocessor 40 that a drive fault has occurred.The second and third, labeled GD1 and GD2, supply pulse width modulatedcontrol signals to the actual gate drive circuits 45 and 47, circuit 45being connected to the gates of transistors Q2 and Q4.

In alternate embodiments, it is possible to achieve a desired variablespeed spindle motor torque settings using a varying analog level, afrequency modulated digital signal, or other approaches, depending uponthe input requirements of the variable speed spindle motor 16.

Those of ordinary skill will recognize that a variety of benefits andimprovements to on-car brake lathes may be achieved through theincorporation of a variable speed spindle motor 16 and the associatedcontrol components of the present invention. For example, themicroprocessor 40 may be configured with software instructions to directthe motor controller 38 to drive the variable speed spindle motor 16 ata variable speed during a vehicle brake resurfacing operation, achievinggreater efficiency and resurfacing consistency. Alternatively, themicroprocessor 40 may be configured with software instructions to directthe motor controller 38 to drive the variable speed spindle motor 16 atone or more sustained speeds during a vehicle brake resurfacingoperation, depending upon the particular procedure for which the on-carbrake lathe is being utilized, or in response to a characteristic of thevehicle brake rotor. Preferably, the variable or sustained speeds atwhich the motor 16 is driven include any speed less than or equal to therated speed of the motor 16.

Utilizing signals received from the motor shaft encoder 50, themicroprocessor 40 may optionally be configured to identify the initialamount of torque exerted by the variable speed spindle motor 16 toinitiate rotation of the output spindle 20 when the on-car brake lathe10 is coupled to a vehicle brake assembly. This initial amount of torqueis associated with a set of parameters identifying the particular inputpower requirements of the motor 16 to achieve the identified torque,which are temporarily stored by the microprocessor 40 in an electronicmemory. The microprocessor 40 may be configured to subsequently utilizethe stored power parameters to provide the motor controller 38 with astarting point for enabling rotation of the motor 16, without requiringthe motor controller 38 to “ramp up” from an minimum power level priorto achieving rotation of the motor 16.

Those of ordinary skill in the art will recognize that a number of theinventive features of the present invention may be implemented in anon-car brake lathe through the incorporation of a fixed-speed motorcoupled to a mechanical transmission having at least two discrete speedsin place of the variable speed spindle motor 16. Selective engagement ofdiscrete drive ratios within the mechanical transmission may achieve twoor more discrete rotational speeds of the output spindle 20, providingfor multiple cutting speeds and linear feed rates.

The present invention can be embodied in-part in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention can also be embodied in-part in theform of computer program code containing instructions embodied intangible media, such as floppy diskettes, CD-ROMs, hard drives, or another computer readable storage medium, wherein, when the computerprogram code is loaded into, and executed by, an electronic device suchas a computer, micro-processor or logic circuit, the device becomes anapparatus for practicing the invention.

The present invention can also be embodied in-part in the form ofcomputer program code, for example, whether stored in a storage medium,loaded into and/or executed by a computer, or transmitted over sometransmission medium, such as over electrical wiring or cabling, throughfiber optics, or via electromagnetic radiation, wherein, when thecomputer program code is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the invention. Whenimplemented in a general-purpose microprocessor, the computer programcode segments configure the microprocessor to create specific logiccircuits.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results are obtained. Asvarious changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A on-car brake lathe system for resurfacing a brake disk of a vehicle brake assembly coupled to a vehicle axle, the brake lathe system having a support structure, an adjustable cutting head secured to the support structure, and an output spindle secured to the support structure and rotationally driven about a drive axis, comprising: a variable speed drive system secured to said support structure, said variable speed drive system having a variable speed spindle motor operatively coupled to said output spindle to rotationally drive said output spindle about the drive axis at a selected variable drive speed; and wherein said variable speed spindle motor is further configured to drive said adjustable cutting head at a selected variable feed rate.
 2. The on-car brake lathe system of claim 1 wherein said variable speed drive system is a direct current motor.
 3. The on-car brake lathe system of claim 2 wherein said variable speed drive system is configured with a pulse width modulation motor controller.
 4. The on-car brake lathe system of claim 2 wherein said variable speed drive system is configured with an SOR motor controller.
 5. The on-car brake lathe system of claim 1 wherein said variable speed drive system is an alternating current motor.
 6. The on-car brake lathe system of claim 5 wherein said variable speed drive system is configured with a vector drive motor controller.
 7. The on-car brake lathe system of claim 5 wherein said variable speed drive system is configured with a motor controller having an inverter circuit.
 8. The on-car brake lathe system of claim 5 wherein said variable speed drive system is configured with a Volts/Hertz drive motor controller.
 9. The on-car brake lathe system of claim 8 wherein said variable drive speed is less than 120 RPM.
 10. The on-car brake lathe system of claim 1 wherein said output spindle variable speed is selected from a plurality of predetermined speeds.
 11. The on-car brake lathe system of claim 10 wherein at least one of said plurality of predetermined speeds is less than 60 RPM.
 12. The on-car brake lathe system of claim 1 further including a manual input signal representing a desired speed of rotation of the output spindle, said variable speed drive system being responsive thereto to alter said variable drive speed to cause the output spindle to rotate at said desired speed of rotation.
 13. The on-car brake lathe system of claim 12 further including a display of the desired speed.
 14. The on-car brake lathe system of claim 12 wherein the variable speed drive system is responsive to a manual input signal to rotate the output spindle at a rotational speed substantially less than the full speed of said variable speed drive system.
 15. The on-car brake lathe system of claim 1 wherein the variable speed drive system includes an electric motor.
 16. The on-car brake lathe system of claim 1 wherein the variable speed drive system includes a transmission having at least two discrete output speeds.
 17. A on-car brake lathe system for resurfacing a brake disk of a vehicle brake assembly, the brake lathe system having a support structure, an adjustable cutting head secured to the support structure, and an output spindle secured to the support structure and rotationally driven about a drive axis, further comprising: a variable speed spindle motor secured to said support structure and operatively coupled independentlv drive each of said output spindle and said adjustable cutting head; a motor controller operatively coupled to said variable speed spindle motor; and wherein said motor controller is configured to control said variable speed spindle motor to selectively drive said output spindle at a variable drive speed and to selectively drive said adjustable cutting head at a variable feed rate.
 18. The on-car brake lathe system of claim 17 wherein said motor controller is operatively coupled to a microprocessor, said motor controller configured to control said variable speed spindle motor responsive to at least one signal from said microprocessor.
 19. The on-car brake lathe system of claim 17 wherein said motor controller is configured to stop rotation of the variable speed spindle motor in response to one or more predetermined conditions.
 20. The on-car brake lathe system of claim 17 where said motor controller is configured to control rotational movement of said variable speed spindle motor through a rotational arc of less than 360 degrees.
 21. The on-car brake lathe system of claim 17 where said motor controller is configured to control rotational movement of said variable speed spindle motor to selectively position said output spindle at one or more rotational positions.
 22. The on-car brake lathe system of claim 18 wherein said microprocessor is configured responsive to a vehicle brake assembly having a parameter greater than a predetermined threshold, to cause said motor controller to regulate the output spindle to rotate at less than a first selected drive speed.
 23. The on-car brake lathe system of claim 22 wherein said microprocessor is further configured responsive to said parameter not exceeding said predetermined threshold, to cause said motor controller to regulate the output spindle to rotate at a second selected drive speed, the first selected drive speed being lower than the second selected drive speed.
 24. The on-car brake lathe system of claim 18 further including at least one input device for providing at least one speed selection signal indicative of a desired speed to said microprocessor; said microprocessor responsive to said at least one speed selection signal to signal said motor controller to drive the output spindle at a drive speed corresponding to said desired speed.
 25. The on-car brake lathe system of claim 18 wherein said microprocessor is configured to determine the torque required to achieve rotation of the output spindle during a first application of power to said variable speed spindle motor.
 26. The on-car brake lathe of claim 25 wherein said microprocessor is further configured to store said required torque, and to establish said stored torque as a starting torque for subsequent applications of power.
 27. The on-car brake lathe system of claim 1 wherein said variable speed spindle motor is further configured to selectively drive said output spindle about the drive axis in a rotational direction selected from between a first rotational direction and a second rotational direction which is opposite from said first rotational direction.
 28. The on-car brake lathe system of claim 17 wherein said motor controller is further configured to control said variable speed spindle motor to selectively drive said output spindle in a selected rotational direction at said variable drive speed, said rotational direction selected from between a first rotational direction and a second rotational direction which is opposite from said first rotational direction. 